Hardware Required

Circuit

None, but the Arduino has to have the Ethernet Shield and a USB cable connected to the computer.

Code

The code below is configured for use with an Ethernet shield, which has an onboard SD slot. In the setup(), we call SD.begin(), naming pin 4 as the CS pin. This pin varies depending on the make of shield or board you are using.

In setup(), create a new file with SD.open() named "test.txt". FILE_WRITE enables read and write access to the file, starting at the end. If a file "test.txt" was already on the card, that file would be opened.

Name the instance of the opened file "myFile".

Once opened, use myFile.println() to write a string to the card, followed by a carriage return. Once the content is written, close the file.

Again, open the file with SD.open(). Once opened, ask the Arduino to read the contents of the file with SD.read() and send them over the serial port. After all the contents of the file are read, close the file with SD.close().

voidsetup(){// Open serial communications and wait for port to open:Serial.begin(9600);while(!Serial){;// wait for serial port to connect. Needed for Leonardo only}

Serial.print("Initializing SD card...");// On the Ethernet Shield, CS is pin 4. It's set as an output by default.// Note that even if it's not used as the CS pin, the hardware SS pin // (10 on most Arduino boards, 53 on the Mega) must be left as an output // or the SD library functions will not work. pinMode(10,OUTPUT);

// open the file. note that only one file can be open at a time,// so you have to close this one before opening another.
myFile = SD.open("test.txt", FILE_WRITE);

// if the file opened okay, write to it:if(myFile){Serial.print("Writing to test.txt...");
myFile.println("testing 1, 2, 3.");// close the file:
myFile.close();Serial.println("done.");}else{// if the file didn't open, print an error:Serial.println("error opening test.txt");}

// read from the file until there's nothing else in it:while(myFile.available()){Serial.write(myFile.read());}// close the file:
myFile.close();}else{// if the file didn't open, print an error:Serial.println("error opening test.txt");}}